Re: [PATCH 1/2] hw/dma: sifive_pdma: Improve code readability for "!!foo & bar"

[Philippe Mathieu-Daudé]

On 9/27/21 04:21, Bin Meng wrote:
> GCC seems to be strict about processing pattern like "!!for & bar".
> When 'bar' is not 0 or 1, it complains with -Werror=parentheses:
> 
>   suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to 
> ‘~’ [-Werror=parentheses]
> 
> Add a () around "foo && bar", which also improves code readability.
> 
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> ---
> 
>  hw/dma/sifive_pdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
> index b4fd40573a..b8ec7621f3 100644
> --- a/hw/dma/sifive_pdma.c
> +++ b/hw/dma/sifive_pdma.c
> @@ -243,7 +243,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
>      offset &= 0xfff;
>      switch (offset) {
>      case DMA_CONTROL:
> -        claimed = !!s->chan[ch].control & CONTROL_CLAIM;
> +        claimed = !!(s->chan[ch].control & CONTROL_CLAIM);

AFAIK in C logical NOT has precedence over bitwise AND, so IIUC
compilers should read the current code as:

           claimed (!!s->chan[ch].control) & CONTROL_CLAIM;

meaning this patch is doing more than "improve code readability",
this is a logical change and likely a bug fix...

BTW GCC suggestions are:

           claimed (!!s->chan[ch].control) & CONTROL_CLAIM;

           claimed (!!s->chan[ch].control) && CONTROL_CLAIM;
>  
>          if (!claimed && (value & CONTROL_CLAIM)) {
>              /* reset Next* registers */
>